When measuring pulmonary function, as in medical and experimental physiological testing on humans or animals, it is desirable to measure lung function by monitoring respiratory patterns.
Existing methods of measuring respiratory parameters include placing an expandable tube around the chest of a human or animal subject. As the subject breathes, the tube lengthens and relaxes as the subject's chest expands and contracts. Strain gauges on the tube are used to determine the volume of expansion of the subject's chest and, from this, a volume of air flow can be derived. A disadvantage of this method is that it only indirectly measures a limited number of parameters. The strain gauge method measures breathing frequency and time for inspiration and time for expiration, but yields no direct measurement of air flow. In addition, the tube may easily come loose, or dislodge completely, causing the measurement quality to deteriorate. In particular, animal subjects, such as dogs, find the tube annoying and they contribute to the loosening and displacement by trying to remove the tube.
Another existing method of measuring respiratory parameters is a magnetometry device. Magnetometry devices are placed on the chest of the subject to measure respiratory parameters. These devices, however, like the strain gauge/tubing devices, measure only limited parameters, and do not directly measure air flow.
A third existing method for measuring respiratory parameters is the whole body plethysmograph, also called a pressure plethysmograph. In this method, the subject is placed inside a box. As the subject in the box breathes and moves air, the changes in the volume and the air flows in the box are measured. Like the methods disclosed above, this method provides only a indirect measure of air flow. It is also somewhat inaccurate. This method cannot be used as a bedside device to monitor the respiratory parameters of someone who is seriously ill, such as those who are anesthetized, in a coma, or in intensive care because they must be able to follow commands. Lastly, the accuracy of the whole body method is limited.
A fourth existing method for measuring respiratory parameters is the spirometer, which works on the basic principle of changing the volume of gas in a container using respiration. The spirometer may be used to measure all the breathing patterns which the devices described above measure. The spirometer, however, is difficult to use on unanesthetized animals. Further, the spirometer cannot be used for exposure experiments, i.e. to introduce gases or particulates, or in clinical situations, i.e. in surgery or emergency situations. In addition, the spirometers available commercially today tend to be expensive compared to other methods of measuring respiratory parameters.
It is an object of the present invention to provide a method and apparatus to measure respiratory parameters directly.
It is another object of the present invention to provide a method and apparatus to measure respiratory parameters as compactly and comfortably as possible in both humans and animals.
It remains desirable to have a means for measuring respiratory parameters accurately and conveniently with a minimum of discomfort to and input from the human or animal subject.